Integration indicating circuit



F. H. SHEPARD, JR

INTEGRATION INDIGATING CIRCUIT Filed Dec. 25, v193e;

Dec. 6, 1938.

Patented Dee. e, 193s PATENT OFFICE y INTEGRATION rNmArlNG clacurrFrancis n. Shepard, Jr., Rutherford, N. J., assignor to RadioCorporation of America, a corporation oi Delaware Application December23, 1936, Serial No. 117,420

2 Claims.

My present invention relates to voltage indicating circuits, and moreparticularly to instantaneous indicating and integration indicatingcircuits having means for weighting input values 5 according to theirmagnitudes.

' The novel features which I believe to be characteristic of myinvention are set forth in particularity in the appended claims; thelinvention itself, however, as to both its organization and lo method ofoperation will best be understood by reference to the followingdescription taken in connection with the drawing in which I haveindicated diagrammatically several circuit organizations whereby myinvention may be carrled into effect.

' In the drawing: A

Fig. 1 isa circuit diagram of a silk thread levenometer embodying theinvention,

Fig. 2 shows the characteristic of the ampli- 20 fier of Fig. 1 betweenthe photo-tube bridge and the first meter, g

Fig. 3 is a schematic representation of the circuit of a welding monitorembodying a modification.

Referring now to the accompanying drawing,

there is shown in Fig. 1 in schematic manner the circuit diagram of aso-called evenometer used in connection with silk threads. The presentinvention will be described in connection with such a device, althoughit need not be used therewith.- Manufacturers of silk articles of wear,such `as hosiery, desire to know as closely as possible the evenness ofthe silk thread. An evenometer indicates the deviations from normaldiameter of silk thread. The transmission of light between spacedparallel threads is measured to determine such deviations. In Fig.. 1,the spaced threads are schematically designated; actually the raw silkthreads are wound around a seriplane board.

40 The length of the latter is divided into panels.

It is, also, equipped with a slot running from one end of the boardtothe other.

A beam of light L is directed through this slot, the beam coming fromlight source 3; The light liii rays passing between threads fall on thecathode 5s mission standard. The latteris replaced by the plifiedvoltage is impressed upon the input elecl0 f trodes of tube I0, thelatter being approximately a square law type amplifier of the 51 type.The output of amplier I0 builds up a unidirectional voltage componentacross the plates of condenser II which component is proportional to theoutput current. Thus, condenser II acts asv an integrator of the outputof amplifier IIl, and the value is taken off the condenser by theelectron discharge tube I2, a triode of the 56 type. 'The output of thelatter includes the meter 2, and the latter is a sensitive recordingmilliammeter. Generally, then, a sexies of bridge unbalances occurringduring a time interval can be totaled and recorded.

Considering the circuit details of my invention more specifically, thealternating current output of the bridge is such that it is zero whenbalanced, and increases directly as the light on cell 4 is varied aboveor below the balance point.

The circuit is so designed that small values of unbalance will vcause noindication, while larger values of unbalance in either direction willcause increasingly larger indications. Fig. `2 shows thischaracteristic. The steepness of the curves can be varied by changingthe sensitivityof amplifier I0. The gap between the curves can bechanged by varying the value of overbias on tube I0 by adjusting theposition of tap I3'on the voltage supply bleeder resistor. The latter isconnected across a +250 volt source, and comprises ve resistor sectionsR1 to R5. The grounded side of resistor R1 is connected by lead I4 tothe low potential side of resistor I5; the condenser I8 connecting thegrid of tube III to the output circuit of amplifier 9.

A condenser II is connected between the cathode of tube I0 and groundedlead I4. The plateof tube I0 is connected to the grid of tube I2 througha resistor I8; condenser Il being connected between the grid andcathodeof tube I2. 50 The grid of the latter is connected to thejunction of resistors Ra and R: through a path including resistor Il,resistor I9, meter I and lead 2li. The screen grid, or second grid, oftube Il) is connected to lead 2li; while the 55 sistor 2I', the latterbeing connected betweeny the plate of tube I2 and the +B side ofresistor Rs. When the alternating current output from the grid amplifier9 is zero, the input grid of tube I is normally biased so that its platecurrent is zero. It follows, therefore, that when meter i' reads zero,the drop across the plate resistor I9 is zero; and the bias voltageapplied to the grid of tube I2 through resistor I8 is equal to thevoltage drop in the resistor section Ra. This is the normal bias of tubeI2, and is obtained under all conditions when switch S is closed. Thus,

when the alternating current is zero there is no tendency for the gridof tube I2 to depart from its normal bias. That is the current inresistor I8 tends to remain zero.

If alternating current is applied from the bridge amplifier 9, currentwill flow in the plate circuit of tube I0; meter I willindicate, andthere will be a potential drop across resistor I9. This latter potentialis applied to condenser II and the grid of tube I2 through resistor I0.The instantaneous current through resistor I0, assuming the timeconstant of resistor I8 and condenser II to be many times the timeunder` consideration, is proportional to the voltage drop across theload resistor I9 of tube III. If the time constant of-resistor I8 andcondenser I I is large with respect to the time under consideration, thevoltage built up across condenser II will be smallwith respect to thevoltage drop in the plate resistor I9. The charge accumulated bycondenser II` during a short period of time will be approximatelydirectly proportional to the voltage drop in resistor I9 multiplied bythe elapsed time.4 If the voltage drop across resistor I9 varies overthe elapsed time, then the charge of condenser I I will be proportionalto the integrated value ofthe voltage drop across resistor I9 multipliedby the interval of time.

It, therefore, follows that if meter 2 is read at definite intervalsafter opening switch S, these readings may be taken as a measure of theaverage voltage drop across resistor I 9. Since the latter is a functionof the bridge unbalance, the reading of meter 2 may be taken as ameasure of average bridge unbalance weighted according to the responsecharacteristics obtained in tube `I0. as shown in Fig. 2. The tap 22 maybe adjusted to make the meter 2 normally read zero,or any other desiredvalue. In this way the average diameter size of the silk threads isdetermined. Before scanning each group of samples the switch Sdischarges condenser II, and clears it so that a new series of additionsmay be made. The bridge being balanced on the average diameter sizetransmits no normal output, but adds up as a measure of unevenness aslong as the/silk does not remain of average size. -Where the skeinstarts to deviate, or an entire skeinvv deviates and becomes coarser orfiner than average, the bridge immediately becomes unbalanced by anamount equal to the extentof deviation.l The output of the bridge, thedeviation current, is then squared and added up so that the meter 2records the i average squared deviation. The tube il may have itsconstants chosen to have a linear law characteristic, or any otherdesired characteristic.

The following list of circuit constants is given merely by way ofspecific illustration, and is not to be considered in any wayrestrictive:

'In Fig. 3 there is shown a welding monitor circuit which embodies theintegrator condenser network employed in the circuit of Fig. 1. In themanufacture of metal tubes, where currents of the order of'75,000amperes are used. the welding machines must be adjusted so that thetotal heat A energy developed in the weld during the welding cycle hasthe correct value. This quantity is measured by the Acircuit of Fig. 3.An air-cored toroidal coil is slipped over one of the welding electrodes3i where it has induced therein a voltage from the ileld of the weldingcurrent. Be-

cause the welding current is a train of approximate sine waves, the coilvoltage is sinusoidal and is proportional to the welding current.

A small part of the open circuit coil voltage, about 0.1 volt, isapplied to a diode 32 in series with a condenser 83. Since the diodecharacteristic for this small voltage has the form of the square law',the current flowing into the con-r` denser is proportional to the squareof the coil voltage, and is proportional to the square of the weldingcurrent. Of course, the device 32 may have any other characteristic. Thecondenser 32 stores up the charge ilowing into it, and thus builds up avoltage which is closely proportionalv to the diode current integratedover the welding period. The condenser voltage is not largel enough todisturb appreciably the proportionality of the diode current to thesquare of the coil voltage.

` Hence, the voltage attained by the condenser 3J is proportional to thesquare of the instantaneous value of the .welding current integratedover the duration of time of the welding period. This integral can betaken as a measure of the total heat energy of the weld, if it isassumed that the resistance of the weld always varies in the same mannerduring1r the welding period.

0n the basis of this assumption, which is approximately correct, thecondenser voltage is read on a vacuum tube voltmeter 34 as a measure o!the total welding heat. This measurement is particularly helpful when awelding machine is first being put into operation. There are twoadjustments to be'made on the machine, one controlling the peak amperageof the welding current and the other the duration of the weldingcurrent. 'Theseadjustments are 'made so that the total heat energy ofthe machines weld has the samevalue as that of other machines turningrout satisfactory work.

While I have indicated and described several systems for carrying myinvention int-o eect, it

will be apparent to one skilled in the art that my invention is by nomeans limited to the particular 1. In an integration indicating vcircuitfor an electrical, current flowing for a predetermined period of time,an electron discharge tube having a substantially square lawcharacteristic, means impressing said current upon the tube inputelectrodes, a condenser in circuit in the space current path of the tubeand4 adapted to be charged up by the output current of said tube, andmeans.

responsive tothe instantaneous magnitude of the potential across thecondenser, for indicating the sum or the squares of the said currentamplitude over said period, said tube including al meter in its platecircuit, andl said indicating means comprising a second tube having itsinput electrodes connected across the condenser.

2. In'an apparatus for measuring the sum of the squares or a currentamplitude integrated over a predetermined time interval, anv electrondischarge devicewhich has a square law characteristic relating input andoutput current, means impressing said current upon said device, acondenser connected to the output circuit of said device whereby thecondenser is charged with the output current of said device, and meansfor translating the instantaneous potential value across the condenserinto an indication of said sum. l,

FRANCIS H. SHEPARD. Jl.

